WHEAT BRAN DIET REDUCES TUMOR-INCIDENCE IN A RAT MODEL OF COLON-CANCER INDEPENDENT OF EFFECTS ON DISTAL LUMINAL BUTYRATE CONCENTRATIONS

To investigate the effects of dietary fibers in colonic luminal physio logy and their role in the prevention of colon cancer, a study was con ducted using two diet groups and two treatment groups in a 2 x 2 facto rial design. The two diets differed only in the type of dietary fiber, wheat bran and oat bran, and the two treatments were injection with t he colon-specific carcinogen azoxymethane, or saline, as a control, Th ere were 34 rats in the carcinogen-injected groups and 11 saline-injec ted rats per diet group. The goal of the study was to determine if a m oderate consumption (6 g/100 g diet) of wheat bran or oat bran would a lter the development of colonic tumors in this rat model of colon canc er, and if the differences in tumor incidence were correlated to lumin al butyrate concentrations, luminal pH or fecal bulk, Short-chain fatt y acid concentrations (SCFA) were measured in feces during the first h alf of the study (the promotion phase of tumor development) and again at the end of the study. Rats consuming oat bran had greater body weig hts (P < 0.002), produced much larger concentrations of all SCFA, incl uding butyrate, in both the proximal and distal colon (P < 0.0001), ha d more acidic luminal pH values (P < 0.0001), but also had significant ly more development of colon tumors (P < 0.03), Alternatively, rats co nsuming wheat bran produced more typical molar ratios of the SCFA (65: 10:20), had a relatively greater concentration of butyrate than propio nate, and produced a larger volume (P < 0.05) and more bulky stool tha n the rats fed oat bran, The results of this study support other evide nce that an acidic luminal pH is not protective in and of itself, and that diets containing wheat bran are protective against colon cancer d evelopment, In addition, these data show that large luminal butyrate c oncentrations in the distal colon alone, as were present in the rats c onsuming oat bran diets, are not protective of tumor development.